It's just a bit of knee-jerk fun, and at times a healthy dose of emotional cringe. I quite enjoy having a look through it after games.
No, it's not horrific. And yes, every fanbase is like that.
I think you may have a point if that is a global fanbase generally being more negative. At least, it would be my guess that local fans, who are "closer to the action", are generally more diplomatic when it comes to all things their club, and that their opinions are to a lesser extent influenced by pundits and TV commentators (who are often shit stirrers by trade). It is my understanding that match going fans are generally the last to call for someone's head, and I can't imagine them posting a lot in match day threads either - kind of a waste of a ticket.
I don't agree that this forum is particularly negative. Knee-jerk, yes, like all football forums. But negative, no. At least not compared to any other football forum, or any forum, or anything internet. If you discount obvious trolls and cry babies, and you take threads that are made for knee-jerkery for what they are (like the match day thread), there's just a lot of opinion.
This is the age of instant gratification, no doubt about that. Still, this is just a football forum. Pretty low-key stuff at the end of the day.
I've never taken the time to count how active any one particular person is in a match day thread, and generally don't take notice of usernames. So I'm just guessing here, but I would think it's mostly just people dropping a line here and there. And because there are a lot of people doing that, you get a long thread. Then during break, they might type some more. If there's anyone who's super-active all the time in the match day thread, then yes, they're obviously not paying attention to the game, or as you say, not actually enjoying football.
Ah, demagoguery. Lovely, lovely demagoguery. There can be no internet debate without it, no matter which 'side' anyone's on.
That is the nature of anonymous human interaction, and it goes for all fans, any sport, or any topic. You think a political forum would be any better? Or a forum on hobby archeology? The level of politeness, honesty and conviction behind what people express behind anonymity will always be lower, and have a bit of a heat-of-the-moment I-don't-see-who-I'm-talking-to aspect to it. You can always ignore the noise, if you want. And if you aren't, well then maybe that's because you find it a bit entertaining after all.